This study will evaluate the benefits and costs of methotrexate therapy in rheumatoid arthritis utilizing data collected annually since 1983 from a panel of RA patients in Northern California. The specific research goals include: l) Determine the efficacy of methotrexate treatment among patients treated continuously with MTX for several years. 2) Estimate a model of the factors that predict the response to methotrexate. The role of patient characteristics such as age, sex, duration of illness, medication history, comorbidities, concurrent medications, prior clinical course, and psychosocial factors will be investigated. 3) Determine the rate of discontinuation of methotrexate, and describe the specific reasons for discontinuation including lack of efficacy and toxicity. 4) Determine the cost- effectiveness of methotrexate (MTX) added to standard therapy. The costs of health care will be estimated from annual data reflecting the utilization of health care services. Outcome will be estimated from data reflecting functional status, severity of disease symptoms, and treatment side effects. 5) Determine the relative cost-effectiveness of MTX compared to other medications used in the routine management of these RA patients using similar methods to determine the efficacy, toxicity, and costs of other medical therapies. A multivariate model will be used to determine the effect of MTX treatment after adjusting for covariates which have an important impact on the course of illness. Information collected from both patients and physicians will be utilized to determine the average rate of discontinuation of MTX, and reasons for discontinuation. A multivariate model will be used to determine the effect of MTX treatment on costs incurred after adjusting for covariates which have a significant impact on costs.